Read our full guide here!
Engine upgrades and transmission conversions began in these Jeeps almost as soon as they rolled off the warships. When Chevrolet introduced the legendary Small Block V8 in 1955, the swap world changed forever.
This guide combines decades of Novak experience and customer success stories. It’s meant to help you plan a clean, reliable, and cost-effective conversion for any “Early” Universal Jeep.
Applicable Models
This article covers GM conversions for these Jeep models:
CJ2A (1946–1949)
The first true civilian Jeep. Compact engine bay — watch engine height for low-hood clearance.
Factory transmission: T90 3-speed
CJ3A (1949–1953)
Similar low-hood setup as the CJ2A.
Factory transmission: T90
M38 (1950–1951)
Military variant of the CJ3A with 24-volt electrical system.
Factory transmission: T90
CJ3B (1953–1964)
“High-Hood” model—taller F-head allows V6 and Vortec options.
Factory transmission: T90
M38A1 (1951–1968)
Predecessor to the CJ5. Steering interference may require Saginaw conversion.
Factory transmissions: T90, T98 4-speed
CJ5 (1955–1971)
The most common early conversion Jeep. All recommended engines apply.
Typical transmissions:
T90 — 134 engine
T98 — rare 134
T86 — 1966–67½ V6
T14 — 1967½–71 V6
CJ6 (1955–1971)
Longer wheelbase allows more transmission options, including:
DJ Dispatcher (1955–1964)
Essentially a 2WD, low-hood CJ — refer to CJ3A notes.
Recommended Engines
GM swaps are clean, proven, and well-supported:
V6 swaps fit better in low-hood Jeeps; V8s are best suited for high-hood or CJ5/CJ6 models.
Transmissions & Adapters
Each of these transmissions can be used effectively with GM power:
Automatic option: TH350 — compact, strong, and ideal for any GM engine.
Adaptable via #103 kit.
Transfer Case
The Dana 18 is the ideal match — compact, durable, and perfectly geared for these Jeeps.
Keep it unless you’re doing something very unusual.
Cooling
For GM V6 swaps, use the KryoFlow Early CJ radiator.
For V8 swaps, the pre-shroud grille must be removed or modified.
Read more on cooling principles.
Mounts & Crossmember
Use Novak adjustable engine mounts for clean fitment.
Rear support: #RMU mount or similar.
Crossmembers can often be reused or redrilled.
Clutch Systems
Two options:
Fuel & Exhaust
Fuel delivery depends on the engine type:
Carb: mechanical or low-pressure electric pump
TBI/TPI: in-tank or inline 40+ PSI pump
LS/Gen. III+: high-pressure EFI setup with return line
Use tight, block-hugging headers with O₂ bungs if running EFI.
Electrical & Gauges
Modern GM engines use a self-contained PCM. Make the engine “think” it’s still in a GM vehicle.
Read about emissions and wiring harness integration.
For gauges:
Factory speedometer works via the Dana 18 VSS pass through
Stock oil, temp, and fuel gauges can be retained or upgraded to electronic.
Steering
The stock Ross system interferes with many swaps.
A Saginaw steering conversion is the cleaner, safer long-term solution.
Summary
There’s no modification that transforms an early Jeep like a well-done GM swap.
With the right parts and planning, the result is a Jeep that’s smoother, stronger, and far more enjoyable to drive.
